High elevated temperature strength nano aluminum-matrix-composite alloy and the method to make the same

ABSTRACT

A novel and unique nano aluminum-matrix-composite alloy that has higher strength between room temperature and 200 degrees C. than those of prior art aluminum alloys and prior art aluminum-matrix-composites. The composite alloy has improved fatigue resistance, wear resistance, a lower coefficient of thermal expansion and higher modules than prior art aluminum alloys.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to high strength aluminum alloys and aluminum-matrix-composites for high temperature applications.

2. Description of Related Art

Aluminum alloys and aluminum-matrix-composites that have high strength at elevated temperature are very useful in aerospace applications and internal engines. In Addition, high elevated temperature strength, high fatigue resistance, high modulus, high wear resistance, low coefficient of thermal expansion are also important for some high temperature applications, such as engine pistons.

It is has been known for several decades that alloys of the Al—Cu—Mg—Fe—Ni type have higher elevated temperature strength and creep resistance than Al—Cu—Mg alloys with the same Cu and Mg content. First used in the form of cast, die-formed or forged pieces, alloys of this type were adapted for production of high-strength sheet metals and were used, in particular, for the fuselage of the Concorde supersonic aircraft. These alloys are also used for pistons in racing engines. They correspond to the Aluminum Association designation 2618, and contain the alloying elements as listed in Table 1.

A piston of an internal gasoline engine must operate for long times at temperatures approaching 200 ° C. Elevated temperature tensile tests conducted on alloys that have been exposed for 100 hours at the test temperature are a means of assessing the suitability of an alloy to perform well as a piston. The typical yield strengths of 2618 aluminum alloy at elevated temperature after 100 hour exposure to temperature are listed in Table 2. To prevent recrystallization, up to 0.25% Mn and 0.25% Zr+Ti has also been added to 2618 as grain refiner. Such variant is registered under the designation 2618A. 2618A improves yield strength at room temperature to 400 Mpa.

The alloy 2618, now used for over 20 years, essentially has a creep resistance compatible with the flight conditions of a supersonic aircraft, but its resistance to crack propagation or fatigue resistance is somewhat insufficient, requiring increased inspection of the fuselage. For the purpose of preparing a successor to the Concorde, a modification of the alloy 2618 was sought in order to improve its resistance to crack propagation. Thus, French patent FR 2279852 in the name of CEGEDUR PECHINEY proposes an aluminum alloy with a reduced iron and nickel content, which has the following alloying elements (% by weight):

Cu: 1.8-3;

Mg: 1.2-2.7;

Si: <0.3;

Fe: 0.1-0.4; and

Ni and Co, where Ni+Co=0.1-0.4 and

(Ni+Co)/Fe: 0.9-1.3.

The alloy can also contain Zr, Mn, Cr, V or Mo contents lower than 0.4%, and possibly Cd, In, Sn or Be contents of at least 0.2% each, a Zn content of at least 8% or an Ag content of at least 1%. This alloy results in a substantial improvement in the fracture toughness factor which represents resistance to crack propagation. Conversely, the results of creep tests at temperatures of 100° C. and 175° C. are entirely comparable to those of 2618.

Bechet in U.S. Pat. No. 5,738,735 proposes a new alloy which has a composition of (% by weight):

Cu: 2.0-3.0;

Mg. 1.5-2.1;

Mn: 0.3-0.7;

Si: 0.3-0.6;

Fe: <0.3;

Ni: <0.3;

Ti: <0.15;

Other elements: <0.05 each and 0.15 total; and

Balance Al.

The alloy can also include a silver content of less than 1%, and in this case, this element can partially substitute for the silicon; the total Si+0.4Ag must be between 0.3 and 0.6%. Preferably, the Cu content is between 2.5 and 2.75% and the Mg content is between 1.55 and 1.8%.

The combination of these various modifications, namely the limitation of the iron and nickel, the increase in the silicon content and the presence of manganese, leads to an unexpected increase in creep resistance relative to the alloy 2618 and to an alloy such as that described in French patent FR 2279852. Note that the fine grained recrystallized structure of light sheet metals represents the most unfavorable condition for creep resistance, particularly for strain under stress, due to the localized strain at the grain boundaries. However this type structure is good for strength properties.

The room temperature yield strength of Bechet's alloy described in U.S. Pat. No. 5,738,735 is average 419 MPa at T6 heat treatment condition, which is little higher than 2618A. However, the creep resistance of the Bechet's alloy is superior to the 2618A at 100 and 150° C.

Good elevated temperature tensile property is not enough for engine piston of lightweight aluminum alloy. A piston that has coefficient of thermal expansion (CTE) close to the CTE of engine cylinder liner made of steel significantly improves engine performance, reduces emission and fuel consumption. Aluminum alloys have a CTE of about 23 PPM/° C., which is too big comparing to about 13 PPM/° C. of steel. High silicon aluminum alloys were developed to reduce CTE of aluminum pistons, such as 380, 390, and 4032. All high silicon alloys have lower tensile strengths than 2618 and Bechet's alloy as show in Table 3. Alloys 380, 390 and Nansa-398 are for cast pistons. Like 2618 alloy 4032 is for forge pistons.

The higher silicon, the lower CTE and the higher wear resistance. However, high silicon aluminum alloys have low tensile strengths and low ductility. The CTE of high silicon alloys is still too high for high-performance engine pistons. All aluminum alloys, including all high temperature alloy and high silicon alloys have low fatigue resistance. In order to further reduce CTE and increase fatigue resistance, aluminum-matrix-composites containing 17% to 25% ceramic reinforcement phase have been introduced to piston application.

The composition of two aluminum-matrix-composites, 2009/SiC/17.5p and 6092/SiC/25p, are listed in Table 4. They contain 17.5 and 25 volume percent silicon carbide ceramic powder. Their elevated temperature strength and CTE are shown in Table 5.

2009/SiC/17.5p and 6092/SiC/25p aluminum-matrix-composites have higher strength at 200° C. than silicon aluminum alloys but still lower than 2618 alloy. They can have lower CTE than silicon alloys and still maintain good toughness. The fatigue resistance of aluminum alloys decrease with stress cycles. Aluminum-matrix-composite can have infinite fatigue life for load under fatigue stress. Table 6 compares the fatigue test data of 2009/SiC/25p at T4 condition with 2024-Al at T42 condition. The composition of 2009 matrix is similar to 2024 composition. The data shows that aluminum-matrix-composites have fatigue resistance of up to 100 times of aluminum alloy.

Peng et al. in U.S. patent application Ser. No. 10/738,275 provided a manufacturing method of three-phase nano aluminum matrix composites. The first phase is aluminum alloy matrix phase. The second is a nano aluminum oxide phase that enhances the strength of the matrix. The third is the micro-ceramic phase that has higher modulus than aluminum oxide and contributes the stiffness enhancement to the composite. This micro ceramic phase also reduces the thermal expansion of the composites and increases the wear resistance. For simplification, the aluminum alloy matrix phase is called as matrix-phase, the nano aluminum oxide phase is called as nano-phase and the high modulus ceramic phase is referred to as modulus-phase. The nano-phase and the modulus-phase are uniformly distributed throughout the matrix to form the nano composite alloy that has high strength and high modulus. Using the three-phase method can significantly improve the strength of an aluminum alloy at room temperature but does not necessarily increase the elevated temperature strength. The present invention specifically addresses the increased elevated temperature strength necessary for high temperature applications.

SUMMARY OF THE INVENTION

It is an object of the present invention to create a novel and unique nano aluminum-matrix-composite alloy (“NAMC-alloy”) that has higher strength between room temperature and 200° C. than those of prior-art aluminum alloys and prior-art aluminum-matrix-composites.

It is another object of the present invention to a novel and unique high temperature strength NAMC-alloy that has higher fatigue resistance than that of prior-art aluminum alloys.

It is still another object of the present invention to a novel and unique high-temperature strength NAMC-alloy that has higher wear-resistance than that of prior-art aluminum alloys.

It is still another object of the present invention to a novel and unique high-temperature strength NAMC-alloy that has lower coefficient of thermal expansion than that of prior-art aluminum alloys.

It is still another object of the present invention to a novel and unique high-temperature strength NAMC-alloy that has higher modulus than that of prior-art aluminum alloys.

It is still another object of the present invention to a novel and unique high-temperature strength NAMC-alloy that can be extruded, rolled, forged and machined into products.

DETAILED DESCRIPTION OF INVENTION

The present invention provides a novel and unique three-phase NAMC-alloy that contains a novel aluminum matrix phase (matrix-phase), a nano aluminum oxide phase (nano-phase) and a micro ceramic modulus phase (modulus-phase). The nano-phase enhances the elevated temperature strength of the matrix-phase. Therefore the resulted aluminum-matrix-composite has high strength between room temperature and 200° C., high modulus, low CTE, high wear resistance, high fatigue resistance. The new high temperature strength aluminum-matrix-composite alloy can be extrude, rolled, forged and machined into finished product.

The novel composition of aluminum matrix, the percentage of nano-phase and the percentage of modulus phase is listed in Table 7. The nano-phase percentage of aluminum oxide is determined by the average particle size of aluminum powder and the powder manufacturing process. Peng et al in U.S. patent application Ser. No. 10/738,275 provided detail method of controlling the percentage of the nano aluminum oxide in aluminum powder. The micron-size ceramic can be micron-size of silicon carbide particles, aluminum oxide particles, boron carbide particles and titanium carbide particles. The ceramic particle size is average 3-30 microns. Silicon carbide is preferred for high thermal conductivity. The powder matrix phase containing aluminum oxide on every aluminum particle is uniformly blended with the micron-size ceramic powder. The blended powder is produced into billet by standard powder metallurgy process.

Example 1

An aluminum matrix of powder alloy containing 2.3% copper, 1.6% Magnesium, 0.35% silicon, 1.4% iron, 1.0% nickel and 1.2% aluminum oxide was blended with 25% of average 7 micron silicon carbide powder. The blended powder was vacuum hot pressed into a 356 mm diameter by 356 mm long billet. This billet was extruded to 95 mm diameter rod. The rod was turned to 89 mm diameter and re-extruded to a 17 mm diameter rod for testing. Tensile sample blanks were cut from the 17 mm rod and were heat treated to a peak strength condition by solution treatment of 530° C. for 2 hours, water quench and age for 2 hours at 200° C. Tensile samples were then machined from the heat-treated blanks. Additional blanks were heat treated to the peak strength condition and then heated to various temperatures for 100 hours before being machined into test samples. The exposure and test temperatures were 150, 175 and 200° C. These data are shown in Table 8.

Example 2

An aluminum matrix of powder alloy containing 4.0% copper, 1.5% magnesium, 0.5% silicon and 0.8% aluminum oxide was blended with 20% silicon carbide. The blended powder is made into an 89 mm diameter billet by vacuum hot pressing. The billet is extruded to a 13 mm diameter rod. Tensile sample blanks were cut from the 13 mm rod and were heat treated to a peak strength condition by solution treatment of 530° C. for 2 hours, water quench and age for 2 hours at 200° C. Tensile samples were then machined from the heat-treated blanks. Additional blanks were heat treated to the peak strength condition and then heated to various temperatures for 100 hours before being machined into test samples. The exposure and test temperatures were 150 and 200° C. These data are shown in Table 9.

The tensile data in Table 8 and 9 show that the new nano aluminum-matrix-composites alloy has significantly higher strength from room temperature to 200° C. than prior art of high temperature aluminum alloys and aluminum-matrix-composites.

TABLE 1 2618 alloying elements (% by weight) Cu Mg Fe Ni Ti Si Al 1.9-2.7 1.3-1.8 0.9-1.3 0.9-1.2 0.04-0.1 0.10-0.25 Balance

TABLE 2 Yield strength of 2618 after 100 hour exposure to temperature Test Temperature (° C.) Room T. 100 150 200 Yield Strength (MPa), 324 310 302 254 T6 Teat Treatment

TABLE 3 Yield strengths of high Silicon alloys after 100 hour exposure to temperature Si CTE Yield Strength (Mpa) Level Elongation (PPM/ at Test Temperature Alloy (%) at R.T. (%) ° C.) Room T. 150° C. 200° C. 380, F 8.5 3 21.5 165 165 152 390, T5 17 1 18.2 210 195 165 NASA 16 0.4 18.8 235 221 198 398, T5 4032, T6 12 9 20.2 315 290 182

TABLE 4 Composites of 2009/SiC/17.5p and 6092/SiC/25p Aluminum- Ceramic Matrix- Composition of Aluminum Matrix (weight % of the Matrix, Al: Balance) (wt % of Total) Composites Cu Mg Mn Fe Si Ti Zn Other, Each SiC 2009/SiC/17.5p 3.8-4.9 1.2-1.8 0.3-0.9 0.3 Max 0.5 Max 0.05 Max 0.25 Max 0.05 Max 17 6092/SiC/25p 0.7-1.0 0.8-1.2 0.15 Max 0.3 Max 0.4-0.8 0.15 Max 0.25 Max 0.05 Max 25

TABLE 5 Yield Strengths of Aluminum-Matrix-Composites after Exposure for 100 Hours at Test Temperature Elongation CTE Yield Strength (MPa) at Test Temperature Alloy at R. T. (%) (PPM/° C.) Room T. 150° C. 200° C. 2009/SiC/17.5p, 8 18 330 295 210 T4 6092/SiC/25p, 3 17.5 427 375 245 T6

TABLE 6 Fatigue test data for 2024-A1 and 2009/SiC/25p AMC. 2009/SiC/25p, T4 2024, T42 (Mill HNBK 5F) Average Cycles to Stress Cycles to Stress Failure (MPa) Failure (MPa) 10,000,000 250 350,000 228 309,000,000 200 1,000,000 207 376,000,000 175 3,500,000 172 10,000,000 155 Data for fully reversed loading, R = −1.

TABLE 7 Composition of the NAMC-alloy of present invention Nano-phase Modulus-phase Composition of Aluminum Matrix (weight % of the Matrix-Phase) (wt % Matrix-phase) (wt % of NAMC-alloy) Cu Mg Mn Fe Ni Si Ti Other, Each Al Al₂O₃ Micro-ceramic 1.0-5.0 0.8-2.0 0.5 Max. 0.01-1.5 0.01-1.4 0.1-1.2 0.01-0.12 0.05 Max Balance 0.2-5 5-30

TABLE 8 Tensile test data for Example 1 NAMC-alloy at temperatures from room temperature to 200° C. after 100 hour exposure. Test Temperature Room T. 150° C. 175° C. 200° C. Yield Strength (MPa) 442 454 351 260 Ultimate Strength (MPa) 589 518 400 302 Elongation (%) 5.1 5.0 7.7 10.3

TABLE 9 Tensile test data for Example 2 NAMC-alloy at room temperatures and 200° C. after 100 hour exposure. TEST TEMPERATURE R. T. 150° C. 200° C. Yield Strength (MPa) 500 454 286 Ultimate Strength (MPa) 531 518 318 Elongation (%) 10 5.0 11.8

Defined in detail, the present invention is a nano aluminum-matrix-composite alloy comprising: high strength at high temperature, high wear-resistance, low coefficient of thermal expansion and high modules, with a matrix phase, a nano phase and a modular phase.

Of course the present invention is not intended to be restricted to any particular form or arrangement, or any specific embodiment, or any specific use, disclosed herein, since the same may be modified in various particulars or relations without departing from the spirit or scope of the claimed invention hereinabove shown and described of which the apparatus or method shown is intended only for illustration and disclosure of an operative embodiment and not to show all of the various forms or modifications in which this invention might be embodied or operated. 

1. A nano aluminum-matrix-composite alloy comprising: high strength at high temperature, high wear resistance, low coefficient of thermal expansion and high modules, with a matrix phase, a nano phase and a modular phase, wherein said matrix phase consists of a weight percent of the matrix phase of 1.0 to 5.0 percent copper, 0.8 to 2.0 percent magnesium, maximum 0.5 percent manganese, 0.01 to 1.5 percent iron, 0.01 to 1.4 percent nickel, 0.1 to 1.2 percent silicon, 0.01 to 0.12 percent titanium, a maximum of 0.05 percent of other elements, and the remainder being aluminum.
 2. (canceled)
 3. The nano aluminum-matrix-composite alloy in accordance with claim 1, wherein said nano phase comprises a weight percent of the matrix phase of 0.2 to 5 percent nano aluminum oxide.
 4. The nano aluminum-matrix-composite alloy in accordance with claim 1, wherein said modular phase comprises a weight percent of the nano aluminum matrix composite alloy of 10 to 30 percent micro-size ceramic.
 5. The nano aluminum-matrix-composite alloy in accordance with claim 1, wherein said micro size ceramic has an average particle size of 3 to 30 microns and is selected from the group comprising silicon carbide, aluminum oxide, boron carbide and titanium carbide.
 6. The nano aluminum-matrix-composite alloy in accordance with claim 1, which is produced by a powder metallurgy process. 